1. Field of the Invention
The present invention discloses methods and reagents for diagnosing and treating glaucoma and related disorders.
2. Description of the Related Art
“Glaucomas” are a group of debilitating eye diseases that are the leading cause of irreversible blindness in the United States and other developed nations. Primary Open Angle Glaucoma (“POAG”), the most common form of glaucoma, is characterized by the degeneration of the trabecular meshwork, leading to obstruction of the normal ability of aqueous humor to leave the eye without closure of the space (e.g., the “angle”) between the iris and cornea (Vaughan, D. et al., (1992)). A characteristic of such obstruction in this disease is an increased intraocular pressure (“IOP”), resulting in progressive visual loss and blindness if not treated appropriately and in a timely fashion. The disease is estimated to affect between 0.4% and 3.3% of all adults over 40 years old (Leske, M. C. et al. (1986); Bengtsson, B. (1989); Strong, N. P. (1992)). Moreover, the prevalence of the disease rises with age to over 6% of those 75 years or older (Strong, N. P., (1992)).
Because increased IOP is a readily measurable characteristic of glaucoma, the diagnosis of the disease is largely screened for by measuring intraocular pressure (tonometry) (Strong, N. P. (1992); Greve, M. et al. (1993)). Unfortunately, because glaucomatous and normal pressure ranges overlap, such methods are of limited value unless multiple readings are obtained (Hitchings, R. A., (1993); Tuck, M. W. et al. (1993); Vaughan, D. et al., (1992); Vernon, S. A., (1993)). For this reason, additional methods, such as direct examination of the optic disk and determination of the extent of a patient's visual field loss are often conducted to improve the accuracy of diagnosis (Greve, M. et al., (1993)).
Glaucoma affects three separate tissues in the eye. The elevated IOP associated with POAG is due to morphological and biochemical changes in the trabecular meshwork (TM), a tissue located at the angle between the cornea and iris. Most of the nutritive aqueous humor exits the anterior segment of the eye through the TM. The progressive loss of TM cells and the build-up of extracellular debris in the TM of glaucomatous eyes leads to increased resistance to aqueous outflow (Lutjen-Drecoll and Rohen 1996; Rohen 1983; Rohen et al. 1993; Grierson and Calthorpe 1988), thereby raising IOP. Elevated IOP, as well as other factors such as ischemia, cause degenerative changes in the optic nerve head (ONH) leading to progressive “cupping” of the ONH (Varma and Minckler 1996; Hernandez and Gong 1996; Hernandez et al. 1990; Hernandez and Pena 1997; Morrison et al. 1990) and loss of retinal ganglion cells (Quigley et al. 2000; Quigley 1999; Quigley et al. 1995; Kerrigan et al. 1997) and axons. The detailed molecular mechanisms responsible for glaucomatous damage to the TM, ONH, and the retinal ganglion cells are unknown.
Current glaucoma therapy is directed to lowering IOP, a major risk factor for the development and progression of glaucoma. These therapies lower IOP, but they do not directly address the pathogenic mechanisms, and the disease continues to progress. At least half of patients with glaucoma are undiagnosed, and by the time patients are diagnosed with glaucoma, they have already lost approximately 40% of their retinal ganglion cells. Therefore, methods for earlier detection and diagnosis of glaucoma are needed.
In view of the importance of glaucoma, and the at least partial inadequacies of prior methods of diagnosis, it would be desirable to have an improved, more accurate method for diagnosing glaucoma in its early stages. In addition, it would be desirable to have new therapeutic agents that address glaucomatous pathogenic mechanisms.